JPH02229716A - superconducting material - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a new oxide superconductor, and relates to a stable superconducting material with a high critical concentration.

[Conventional technology]

Perovskite steel oxide (KzNi F4 type Laz-xBaxcuo4) exhibits superconductivity at relatively high temperatures.
) was invented in 1986 by Bednorz and Muller. After that, the basic structure of perovskite, AB
Various superconductors have been synthesized by replacing A-site ions with large ionic radii (La8+ and Ba''+ in the above example) in Oa.A typical example is La-Sr. -Cu-0 (critical temperature Tc=4
0K), Y-Ba-Cu-0 (Tc=90K). As a substance with even higher Tc, Ba-
Ca-T1l-Cu-O (Tc=120K), Sr-C
a-Bi-Cu-○ (Tc=105K) and T
Q-Sr-Cr-C u-0 (Tc= 1 1 0 K
) Superconductors were invented. La-Sr-Cu-0 or Y-Ba-Cu-0 superconductors are relatively easy to synthesize, but their Tc is low, and the focus of research is on TQ-Ba.
-Moving to Ca-Cu-0, TQ-Sr-Ca-Cu-0 and Bi-Sr-Ca-Cu-0 superconductors. - The Bi-Sr-Ca-Cu-0 based superconductor is
There was a drawback that phases with low TO tend to coexist in one crystal grain, making it extremely difficult to obtain a single phase, and as a result, critical current density could not be increased. TQ-Ba-C
The a-Cu10 and TQ-Sr Ca-Cu-○ superconductors have the drawback that Tn evaporates during firing, making it difficult to control the composition of the final product. [Problems to be Solved by the Invention] Among the conventional superconducting materials mentioned above, those that are relatively easy to synthesize do not have a sufficiently high Tc, and materials with a high Tc are difficult to synthesize. Among the superconductors with a perovskite-like structure discovered so far, La1-. Ba. CuOx is T
The defect was that c was as low as 30K.

Y B a zc u 80x has Tc of 90K. At this level of Tc, it is difficult to use it at liquid nitrogen temperature, and it also has the disadvantage that it easily reacts with moisture and carbon dioxide gas and deteriorates. The Bi-Sr-Ca-Cu-0 superconductor has the crystal phase BizSrzCa that gives the highest Tc and IIOK among them.
It was extremely difficult to synthesize a material consisting only of zCua○, and there was a drawback in that it was impossible to create a superconductor material with a high critical current density.

TQ-Ba-Ca-Cu-0 and TQ-Sr
The -C a -C u-0 superconductor has the drawback that evaporation of 'rQ occurs during firing, making it difficult to control the composition of the final product. The object of the present invention is to have a high critical temperature and to
By providing superconducting materials with chemical properties,
The objective is to provide a superconducting material that has a high critical temperature, a high critical current density, a high critical magnetic field, is chemically stable, and is easy to manufacture. [Means for Solving the Problems] The present invention provides a composite oxide having the general formula (At-xA'X)2B2B'n-tcun○
2n+4+δ or (At-xA'X) B 2B
I n-tcunozn+a+δ Here, A: Bt or TΩ A': Ionic radius in the crystal is 0.81 or more 1.0
Single or multiple elements B: Na, K, Rbt Cs, MgtCa, Sr,
At least one of Ba B': At least one of Na, Ca, Y, and lanthanite elements.

Cu: Copper ○: Oxygen is a compound represented by n=2.3 or 4 −1 <δ<1.0≦X≦1, and its crystal structure has five oxygen ions surrounding the Cu ion, forming a pyramid. A superconducting material containing a type-coordinated portion and having an average copper valence of more than 2.0 and less than 2.5. The first crystal structure of high-temperature superconducting materials discovered so far
This is summarized in Figures 3 to 3. Among these crystal structures, the first
Superconductors with the structures shown in Figures (2) and 2 (2) have particularly high Tc. Superconductor Lat-xBaxCuOx, La having the structure shown in Fig. 3 (1)
t-x S r xC u Ox and L a i-
In the case of superconductor YBazCuaO7-δ having the structure shown in FIG. 3(2), there is a third
It was known that the relationship shown in the figure exists, and that there is an optimal average valence of Cu. This time, we found that an optimal average Cu valence similarly exists in superconducting materials with crystal structures different from those shown in Figure 1, and within certain conditions, They discovered that superconductivity is preserved even if each site in the crystal is replaced with another element, leading to the present invention. In the case of the superconductors discovered so far with the crystal structure shown in Figure 1 or Figure 2, the A and A' sites were occupied only by TQ or Bi. However, even if this site is replaced with another atom, if the crystal structure does not change and the average valence of Cu is within the range of 2.0 to 2.5, superconductivity can be achieved. We found that this shows that Similarly, materials in which other sites are replaced with other atoms also exhibit superconductivity.

We also carried out crystal structure analysis of various materials synthesized by replacing each site with other atoms, and investigated in detail the interatomic distance between Cu ions and O ions that form the Viramit type. Conventionally, Cu-○ spreads in the plane direction of a pyramid shape.
It was said that the bond between Cu and oxygen ions is strongly related to superconductivity, but according to our research, there was a strong correlation between superconductivity and the distance between Cu ions and oxygen ions that exist in the vertex direction. Specifically, the distance is 2.10 people or more and 2.30 people.
He discovered that substances smaller than a human being have excellent superconductivity.

The superconducting material of the present invention is provided in the form of a powder, a lump, a sintered body, a thick film, or a line. When the substance of the present invention is synthesized by mixing and reacting the starting materials by some means, powders, lumps, etc. are obtained. After the powder is shaped, it can also be obtained as a sintered body. It is also possible to form a thick film using the doctor blade method. A tape or ribbon-shaped superconductor can be obtained by melting the powder and rolling it with a roll.
A wire-shaped product can be obtained by filling a metal pipe or the like and drawing or rolling it. In order to obtain the superconductor of the present invention in the form of a thin film, a sputtering method, a vapor deposition method, a thermal spraying method, a laser vapor deposition method, an MBE method (Molecular BeamEpita method), etc.
xy), C V D method (Chemical Vav
ordoposition) etc. are used. In order to obtain the superconducting material powder of the present invention, methods such as the oxide mixing method, coprecipitation method, and sol-gel method can also be used. The temperature when reacting raw materials to synthesize a superconducting material varies depending on the composition of the material and the manufacturing method, but is between 600°C and 100°C.
A range of 0°C is suitable. Generally speaking, the larger the number of n, the longer the reaction time is required at a lower temperature. [Operation] High-temperature superconducting material Lat-xB whose Tc does not exceed IOOK
axcuox, Lat-xs rxcuox, YBaz
In CuaOr-δ, research on its superconducting mechanism is also actively conducted. Lat-xDxcuo
The superconducting materials represented by the composition formula x (D: Ba, Sr, Ca) all have crystal structures as shown in Figure 3 (1), and the elements represented by D are Ba, Sr,
Any type of Ca exhibits superconductivity. Also YBaz
The superconducting material represented by the composition formula CuaOfu δ has the crystal structure shown in Figure 2 (2), and this is also a material in which Y atoms are partially or completely replaced with other rare earth elements. It is known that as long as the crystal structure does not change significantly, it exhibits superconductivity. Based on these facts, it is currently believed that the crystal structure of the material, especially the plane of Cu atoms and ○ atoms extending in the direction perpendicular to the C axis, holds the key to the development of superconductivity, and new superconducting materials are being developed. Research is also progressing with this point in mind regarding the search for. On the other hand, it is known that the Tc value changes depending on the DJi substitution rate for the L a l-x D x C u O x system and the oxygen vacancy amount δ for the YBaxcuso7-δ system. Currently, this is related to the average valence of Cu, and it is said that Tc strongly depends on the average valence of Cu (see Figure 4). Regarding superconducting materials having the crystal structure shown in Figure 3 and having Tc not exceeding IOOK, it is thought that the crystal structure and the average valence of Cu have a strong influence on superconductivity. However, until now, no such knowledge has been obtained regarding other crystal structures, a group of superconductors with the structures shown in Figures 1 and 2. In this study, we synthesized many types of materials with these crystal structures, examined the crystal structures and hole concentrations in detail, and found common characteristics among materials that exhibit superconductivity. The ions occupying the sites shown in (A) in the crystal structure model of Figures 1 and 2 do not particularly contribute to the development of superconductivity, and unless the crystal structure is changed, any element may be used. I found out that it doesn't matter. Next, regarding the role of the ions occupying the site shown in (B) in the model of Figures 1 and 2, it is clear that oxygen, which is the closest neighbor of the cations occupying this part, is deeply involved in superconductivity. We found out. Figure 5 shows a graph in which the horizontal axis represents the distance between the Cu ions forming a pyramid and the oxygen ions located at the apex of the pyramid, and the vertical axis represents Tc. It can be seen that there is a clear correlation between the superconducting critical temperature and this distance. The easiest way to change the interatomic distance in this region is to introduce an element with a different ionic radius into the (B) site. We found that the ion radius occupying the (B') site must be greater than or equal to 0.90 and less than 1.0. If the size of the ions in this part is large, oxygen will be introduced and a pyramid of Cu atoms and OyK atoms will not be formed. Also, if it is too small, the crystal structure will be different. The above results were obtained by synthesizing various superconducting and non-superconducting materials and examining them in detail, but superconductivity does not occur just by satisfying these conditions. We found that in superconducting materials with the structure shown in Figures 1 and 2, Tc changes depending on the concentration of holes existing in the pyramid structure formed by Cu atoms and OM atoms. ．． Various elements A, A', B, B' and various X
The composition (Ai-xA'x)zBzB' z
Synthesize the substance CuaOro+δ, and determine the hole concentration and Tc
We investigated the relationship between The value obtained by subtracting 2.0 from the average valence of Cu gives approximately the hole concentration. 5th result
As shown in the figure. Tc is highest when the hole concentration is around 0.22, and Tc is 60 when the hole concentration is below 0.08 and above 0.38.
It can be seen that it is below K. If it is possible to synthesize a substance that satisfies the conditions related to the crystal structure and the hole concentration described above, it is considered that there is a high possibility that superconducting substances other than the substance discovered in the present invention can be obtained.

However, as there is currently no clear answer regarding the mechanism by which superconductivity occurs, there is no guarantee that a material will become a superconductor just by satisfying these two conditions. However, the principles of the present invention will provide important guidelines for the discovery of new superconducting materials.

〔Example〕

Example I TQzOs. Bizoa, S ro, Cab, and CuO were used as starting materials. First of all, BizOatSr.
o, Cab, and CuO respectively Bi:Sr:Ca:Cu
The atomic ratio of . Mix in a ratio of 1:2:1:2, 88
It was fired in the air at 0°C for 100 hours. During the process, the material was removed from the furnace, cooled, and crushed three times. TnzOs was added to the powder thus obtained, TQ:Bi:Sr:Ca:
They were mixed so that the atomic ratio of Cu was 1:1:2:1:2, sealed with gold foil, and fired at 870°C for 50 hours. The finished powder XI! Analysis of the diffraction pattern confirmed that this is a new material with a crystal structure similar to BizSrxCaCuzOx, with 50% of the Bi sites replaced by TQ. When this powder was sintered at 800°C and the electrical resistance of the resulting sintered body was measured while lowering the temperature, the resistance began to drop rapidly at around 90K. 80
At K, the resistance value became zero. Example-2 (B it-xA' xbs r zc a zc
Synthesis was carried out according to the method described in Example 1 to obtain a substance represented by the compositional formula of u IIOX, and the Tc of the sample was measured. The results are shown in Table 1, and the Tc shown here is . The temperature at which resistance begins to drop rapidly, i.e. T
c The onset temperature is shown in absolute temperature. Table 1: Example 3 Raw material oxides were mixed to obtain a substance represented by the composition formula B is(S rt-xBx)zcazcuao+t, various samples were synthesized, and their Tc was measured. The results are shown in Table 2. Table 2, Figure 7 shows the hole concentration (value obtained from Hall coefficient measurement) of the prepared sample, and the C of the pyramid part in the crystal.
The relationship between u (value converted to the number per unit) and Tc is shown. FIG. 8 shows the relationship between hole concentration and Tc.

Example-4 Bizs rz (Cat-xB' x)zcusox
Raw material oxides were mixed and calcined to obtain a substance represented by the composition formula, and various samples were synthesized and their Tc values were measured. The results are shown in Table 3.

Table 3 I made a decision. The results are shown in Table 4.

Table 4 Example-5 (T Q t-xA' X)2B azc azc
Mix and sinter raw material oxides to obtain a substance shown by the compositional formula of u sox, synthesize various samples, and measure their Tc Example-6 Compositional formula of TQ (Bat-xBx)zcazcua○8 The raw material oxides were mixed and calcined to obtain the substance shown in , and various samples were synthesized and their Tc was measured. The results are shown in Table 5. Table 5: After firing, the Tc was measured. The results are shown in Table 6. Table 6 also shows the relationship between hole concentration and Tc for these samples.
As shown in the figure.

Comparative Example-1 In order to prepare a sample with a low hole concentration, T Q (
B a 1-1-L a x)zc o zc u a
The raw material oxides are mixed to obtain the substance shown by the compositional formula of Ox, and the hole concentration and T of these samples are
Figure 9 shows the relationship between c. Example 7 Raw material oxides were mixed and fired to obtain a substance represented by the compositional formula of (TQI-XA' The results are shown in Table 7. 7 4× Table 8 Example-8 A superconducting material having the crystal structure shown in FIG. 1 (3) was synthesized, and its Tc was measured. Table 8 shows the results.

Example 9 A superconducting material having the crystal structure shown in FIG. 2 (3) was synthesized, and its Te was measured. Table 9 shows the results. Table 9 [Effects of the Invention] According to the present invention, improvements in various properties required of superconducting materials such as critical temperature, critical magnetic field, current density, chemical stability, and formability can be expected.

[Brief explanation of the drawing]

FIG. 1 (1) to (3) show the compositional formula AzBzB' n-t
Schematic diagram showing the crystal structure of a superconducting material represented by C n O 2n + 4,000 δ (n = 2.3.4), Figure 2 (1)
~(3) is the compositional formula A B zB 'n-ICfiO
A schematic diagram showing the crystal structure of a superconducting material given by zn ÷ 3,000 δ (n = 2.3, 4), Figure 3 (1) and (2) are L
a t-xDxC u OX (D: Ba, Sr, Ca
) and YBa2CuaOn-δ, and FIG. 4 shows the relationship between the average valence of Cu and the critical temperature ('re) of L a l-x D x C u O x and YBazCuaO7-δ. Characteristic diagram, Figure 5 is a characteristic diagram showing the relationship between Tc and the distance between Cu atoms forming the pyramid part of the superconducting material according to the present invention and oxygen atoms located at the apex part, and Figure 6 is a characteristic diagram showing the relationship between Tc and the superconducting material according to the present invention. FIGS. 7 to 9 are characteristic diagrams showing the relationship between the hole concentration of the substance and Tc, and FIGS. 7 to 9 are characteristic diagrams showing the relationship between the critical temperature Tc and the number of holes per Cu atom in the pyramid portion.

Claims (15)

[Claims] 1. General formula (A_1_-_xA'_x)_2B_2B'_n_-_
1Cu_nO_2_n_+_4+δ(A_1_-_xA
'_x)B_2B'_n_-_1Cu_nO_2_n_
+_3+δ where A: Bi or Tl A': An element whose ionic radius in the crystal is 0.81 Å or more and 1.05 Å or less, singly or in combination, B: Na, K, Rb, Cs, La, One or more selected from Ca, Sr, Ba B': One or more selected from Na, Ca, Y, lanthanoid elements Cu: Copper, O: Oxygen n: 2, 3 or 4 −1<δ<1 , 0<x≦1, wherein the average valence of copper in the crystal is greater than 2.0 and less than or equal to 2.5. 2. 2. The superconducting material according to claim 1, wherein the crystal structure of the material includes a portion in which five oxygen atoms are arranged around Cu in a pyramid shape. 3. 3. The substance according to claim 2, wherein the number of holes in the substance is per piece of copper in which five oxygen atoms are coordinated in a pyramid shape,
A superconducting material characterized by having 0.15 or more and 0.35 or less. 4. 3. A superconducting material according to claim 2, wherein the crystal structure of the material is as schematically shown in FIG. 1 or 2. 5. 3. The superconducting material according to claim 2, wherein the element constituting A' is one or more of Bi, Tl, Ca, Pb, Hg, Y, and lanthanide elements. 6. 3. The superconducting material according to claim 2, wherein the elements constituting B and the elements constituting B' are regularly arranged in the crystal. 7. The substance according to claim 4,
In the schematic diagram of the crystal shown in the figure, atoms constituting A and A' occupy the part indicated as (A) site, and (B) site and (B'
) The atoms constituting B and B' occupy the part indicated as site, Cu occupies the part indicated as (C) site, and (D
) A superconducting material characterized by having a crystal structure in which oxygen occupies the portions indicated as sites. 8. The substance according to claim 7,
Cu occupies the part indicated as (C-1) in the figure, and (D-
1) A superconducting material characterized in that the distance between oxygen sites occupying the portion indicated by 1) is 2.10 Å or more and 2.70 Å or less. 9. A superconducting wire comprising the substance according to any one of claims 1 to 8. 10. A magnet using an element containing the substance according to any one of claims 1 to 8. 11. A device comprising the substance according to any one of claims 1 to 8. 12. A measuring device using an element containing the substance according to any one of claims 1 to 8. 13. An arithmetic device using an element containing the substance according to any one of claims 1 to 8. 14. A power storage device using an element comprising the material according to any one of claims 1 to 8. 15. A magnetic shielding device using the material according to any one of claims 1 to 8.